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Chapter 2.3
Chemical Pollutants
• Humans have been introducing synthetic
(man-made) chemicals into the environment.
Some examples are:
PCBs (polychlorinated
biphenyls) widely used in
paints, plastics, lubricants up
to 1977
DDT (an insecticide for
mosquitos) now banned in
many countries
Dichloro-diphenyl trichloroethane
DDT was first used in WWII
to protect against diseases
such as typhus and malaria.
It is cheap and effective as
an insecticide – so it began to
be manufactured for home
Before it was banned in 1972
by the EPA for use in
agriculture, 1,350,000,000
pounds of DDT had been
made in North America.
• DDT is found to have
estrogenic effects:
– Causes reproductive
– Weakens the shells of
eggs (eggs break or do
not hatch)
– Can also cause nervous
system/ immune system
disorders in animals
DDT – Used as an Insecticide
• DDT is used today in such
African nations as
Zimbabwe and Ethiopia to
control mosquitoes and
the tsetse fly.
• These two insects cause
serious diseases, such as
malaria and sleeping
• Used widely in products like
paints, plastics, etc as softening
agents from the 1930’s – 1970’s
• Banned in North America in 1977
• There are 209 different congeners
(different chemical structures)
• PCBs interfere with immune
function making an organism
more susceptible to disease
(ex: cancer)
Heavy Metals
• Heavy metals are metallic
elements that are toxic to
– Levels of lead in the soil have
increased due to human
• Lead is not considered safe
at any level.
• Many electronics contain
lead and must be recycled
• Lead can cause anemia and
nervous and reproductive
system damage.
Heavy Metals (con’t)
– Cadmium is also found in low levels naturally.
• Cadmium is used in the manufacture of plastics and
nickel-cadmium batteries.
• It is toxic to earthworms and causes many health
problems in fish.
• In humans, the main source of cadmium is exposure to
cigarette smoke.
– Cadmium causes lung diseases, cancer, and nervous
and immune system damage.
Heavy Metals (con’t)
– Mercury also is found naturally.
– Mercury has entered ecosystems through the burning of fossil
fuels, waste incineration, mining, and the manufacture of items
like batteries.
• Coal burning accounts for 40 percent of the mercury released into the
– Mercury bioaccumulates in the brain, heart and kidneys of many
• Mercury compounds
bioaccumulate in fish, adding
risk for any organisms eating
Persistent Pollutants!
• Both DDT and PCBs are called
“persistent organic pollutants” (POPs)
• This is because they take a LONG time
to break down
HALF-LIFE = the time it takes for ½ the
substance to break down
Half-life (PCBs) = 8 -10 years
Half-life (DDT) = 15 years
• Bioaccumulation is the “build-up of
chemicals in living organisms”.
• The chemical accumulates because it
does not break down easily
(decomposers can’t break them down)
• The chemicals get stored in fat-cells of
organisms and can cause serious
NOTE: Accumulation is measured in parts per million (ppm)
Bioaccumulation - EFFECTS
• How it affects organisms:
– Birth defects
– Failure to reproduce
• Amphibians live on both land and in the water.
– Amphibians are sensitive to chemical changes in the
environment and are valuable indicators of environmental
– Since the 1980s, many of the world’s amphibian species
have suffered declines in population.
– There also have been alarming increases in amphibian birth
Amphibians, like this frog, have exhibited drastic changes
since the 1980s.
Many theories attempt to explain these changes, including
drought, increased UV rays, pollution, habitat loss, parasites,
and diseases.
How BIOACCUMULATION affects ecosystems:
If an important part of the food chain cannot
reproduce, the whole food chain is affected.
Keystone species = species that can
greatly affect population numbers &
health of ecosystem.
Biomagnification is
the process where
chemicals accumulate
AND become more
concentrated at each
trophic level of the
food chain.
ORCAS- Biomagnification
• The PCB load of orcas (whales) is
the highest of any animal in the
• PCBs concentrate in the blubber of
the whale
• When the blubber is burned for
energy, the PCBs are released into
bloodstream (where they affect
immune function).
• Calves are born with the same PCB
level as mother and then obtain
more through milk.
• PCB’s will affect the reproductive
cycles of orcas until at least 2030.
Reproductive success of BC’s resident orcas may be affected until 2030
Undoing the Damage
• Science has found ways of reducing the effects of
chemical pollution on the environment...
Using living organisms (plants, bacteria) to naturally
cleanup chemical pollutants through biodegradation
Chemical-eating bacteria and
micro-organisms can break down
chemicals into non-toxic
Rhodococcus bacteria can
biodegrade PCBs
Bacteria can be used to clean
up oil spills and underground leaks
A Bright Idea!
Recently, scientists
were able to change
a gene in these
bacteria allowing
them to fluoresce
(glow) when they are
in contact with oil or
other chemical
Bioremediation With Plants
• Plants can also be used to help
trap hazardous wastes such as
heavy metals
• The plants uptake the metals
and trap them in their tissues
• Plants also help stabilize by
reducing wind and water erosion
(that would spread